1) Field of the Invention
The present invention concerns a process for the detection of obstacles and, in particular, the detection of obstacles in front of an automotive vehicle, together with an apparatus to carry out the process.
2) Discussion of Related Art
Processes for detecting obstacles with a video camera on board vehicles and producing a video image of the scene in front of the vehicle, are known.
However, in order to ascertain the position of a point within the space of the scene with a single camera, it is necessary to introduce models of the environment for comparison. With such a process it is not possible to determine the distances of potentially dangerous obstacles.
Another process for the detection of obstacles uses two or more video cameras thus permitting the acquisition of more complete information on the scene facing the vehicle, in a zone relatively close to the vehicle up to about 20 meters. However, this process does not make it possible to determine precisely the distances of obstacles, due to the fact that the error in the distance detection, in the viewing direction, is proportional to the square of the distance.
It is an object of the present invention to eliminate the disadvantages of the known processes mentioned above by providing a process for the detection of obstacles present in front of an automotive vehicle, the process making it possible to determine with precision the position of a point in space relative to a reference associated with the vehicle and to allocate different points in space to an obstacle and to ascertain their position in a zone extending, for example, from 5 to 85 meters.
For this, the process for the detection of obstacles present in front of, in particular, an automotive vehicle, includes providing, by means of a video camera on board the vehicle, a composite video signal representative of a video image of a scene in front of the vehicle, measuring the distances of the obstacles in the scene relative to the vehicle by means of a ranging apparatus also present on board the vehicle, the pulsed incident waves of which sweep the scene by successive horizontal telemetric lines, and synchronizing the pulsed emission of the incident waves and their scan by scanning field synchronization signals and the line signals extracted from the video signal.
According to a characteristic of the invention, the telemetric data of the telemetric apparatus, which are representative of the measured distances of the obstacles and the coordinates of the points of impact of the incident pulsed waves, are entered in or overlaid on the video image in a synchronized manner.
Advantageously, the pulsed emission of the aforementioned incident waves is effected during the uneven field of each video image and the telemetric data are entered during the following even field of the video image.
According to another characteristic of the invention, the pulsed emission of the incident waves is carried out at a first, predetermined clock frequency, obtained from the frequency of the line synchronization signal. At least the telemetric data relative to the distances of the impact points measured are digitalized during the uneven field of the emission of the pulsed waves at a sampling frequency equal to the first clock frequency. Further, the digitalized telemetric data are stored during said uneven field with a combination of the first clock frequency and a second clock frequency. In order to avoid data conflicts, the inscription of the digitalized data occurs during the following even field onto a certain number of consecutive video lines of the even field at a third clock frequency obtained from the frequency of the line synchronization frequency, said third clock frequency being higher than the first and second clock frequency.
The aforementioned pulsed waves horizontally scan a telemetric line of the scene during an uneven frame at the first clock frequency. Then, the beam of pulsed waves is deflected vertically and horizontally during the even field according to an initial scanning position of a following telemetric line, the scan being effected during the uneven field of a following video image.
Preferably, only the values in the coordinates x, y of the initial position of each scan of a range line are digitalized and placed into memory at the end of the even fields and the positions of the different impact points of consecutive pulsed waves are automatically reconstituted from a pre-established scanning curve, preferably a ramp.
According to another characteristic of the invention, a signal of the selection of the number of the aforecited video lines upon which the range data are inscribed is produced at the onset of each even field, and shortly after the selection signal, a signal of the validation of the entry of the range data on the video lines selected is produced.
Advantageously, the aforementioned video lines upon which the range data are inscribed are located in the upper part of the video image after several forced black lines and a forced white general starting line, and they comprise a line for the identification number of the video image and the lines proper for the inscription of the range data.
The range data and the video image signal are recorded on a recording device, such as a video tape recorder, or else the range data and the video image are processed in real time.
The points of impact of the pulsed incident waves are disposed in zigzag by the temporary dislocation of one range line in two at the onset of each horizontal scan.
The invention also proposes an apparatus for the detection of obstacles to carry out the above-described process.
The apparatus according to the invention comprises a video camera on board of the vehicle for viewing a scene in front of the vehicle, a range apparatus to measure the distance of the obstacles in the scene relative to the vehicle, an assembly for the deflection of the pulsed radiation emitted by the range apparatus with at least one controlled mobile deflection mirror to cause the radiation to carry out a scanning movement of successive horizontal telemetric lines on the scene, and a signal conditioner to produce, from the synchronization signals of the line pattern and the video signal of the camera, signals making it possible to command, in the same uneven field, the emission of pulsed radiation and the horizontal scanning movement of the mirror and the production of signals to inscribe, during the following even field onto successive lines of the video image, the range data relative to the coordinates of the points of impact of the pulsed radiation on the obstacles of the scene and the distance measured of each impact point relative to the vehicle.
Preferably, the apparatus comprises two mobile deflection mirrors for horizontal and vertical scanning. The displacement of the horizontal deflection mirror scans along a range line. A loop circuit locked in phase and a certain number of dividing circuits controlled by the line synchronization signals produce a first clock frequency to command the emission of pulsed radiation and the digitalization of the range data, a second clock frequency, preferably at a frequency double that of the first clock frequency places the range data into a memory and a third clock frequency causes the inscription of the range data onto the video image.
The conditioner includes electronic circuits capable of producing a first signal which appears prior to the onset of an uneven field and ending with said uneven field to define a window permitting the measurement of data relative to the initial positions of the vertical and horizontal deflection mirrors prior to the scanning of a range line, i.e., the horizontal scanning, the emission of pulsed radiation and the incrementation of the vertical scanning mirror to a subsequent range line, with a second signal emitted after the start of each pair of frames making possible the selection of the number of video lines onto which the range data are inscribed, and a third signal emitted shortly after the appearance of the second signal, to validate the inscription of the range data onto the video lines selected.
The conditioner further contains a locking or clamping stage making it possible to produce so-called clamping pulses for the correct alignment of the video and range signals.
Advantageously, the apparatus comprises decoupling means, such as a cover in the form of a plate, for decoupling the emission or the reception of the pulsed radiation to the level of the aforementioned mirrors.
Preferably, the above-mentioned range apparatus is of the laser type.
The apparatus may further comprise a computer on board the vehicle for processing the range and video data and for producing signals intended to control the safety devices of the vehicle.